hydraulic coupling

A hydraulic coupling is a device that uses a liquid, typically oil, to transmit rotational motion and torque between two shafts. It consists of a vaned impeller on the drive shaft and a vaned runner on the driven shaft, both enclosed in a liquid-filled casing.1

When the drive shaft rotates, it imparts kinetic energy to the liquid, which then turns the runner on the driven shaft. In a properly designed coupling, the driven shaft rotates at a speed slightly less than the drive shaft, usually about 3% slower under normal loads. A key feature is the absence of a direct mechanical connection, which means hydraulic couplings do not transmit shocks or vibrations. They are also known as fluid couplings.12